import java.util.Scanner;

public class SumRecursion {
    public static int Recurision (int a){
        return(a <= 1 ? 1 : a + Recurision(a-1));

    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int ret = scanner.nextInt();
        System.out.println(ret + "的前n项和为"+Recurision(ret));
    }
}
